The vids are a blast to make and glad you guys enjoy them. There are so many atmospheric sounds in railroading....seems impossible for manufacturers to replicate them accurately in any scale.
It is easy to take some sound from a Youtube vid and apply it to your movie in windows movie maker. Here is how:
1. Find a train vid on Youtube that is roughly 2-4 minutes. Shorter ones create smaller MP3 files that are easier to import into Windows Movie Maker. I also look for vids without people talking in the background etc. It must have good sound quality.
2. Once you choose the vid, simply cut and paste the link to the vid into this free online program:
http://www.youtube-mp3.org/
3, The program will convert the audio to MP3 which you can not only use for train vids but also atmospheric sounds on the layout. Download the MP3 file o your computer and save it somewhere you can easily find it.
4. Next, time the approach of the engines in seconds. So if it takes 40 seconds from the time of the real vid starts to when the engines pass the camera then this tells me how long I need to wait to sync the model with the audio. I pull my train up to the camera so the lead engine is at a point where it is even with the camera. Then I back it up for 40 seconds using my timer. Once stopped, I reset the watch and bring it back to the camera within the 40 second time frame and allow it to run completely past the camera this time. The trick with this particular shot was the grade coming back. In the first try the train was way late as it was coming back up the hill. A few more tries and it worked out.
5. Lastly, take your completed vid and open it up in windows movie maker. Its usually free bundled software with windows. Open the vid in movie maker and click the "add music" button. Choose the MP3 you created and downloaded to your computer. Then save and you are set!
Its really pretty easy.....Bill I am glad you enjoy them on the big screen. I am going to buy a new camera in the spring and the quality will improve quite a bit. 
I felt like I was standing at the CSX/NS overpass at Collier Yard in Petersburg Va.
